Percutaneous electrode

ABSTRACT

Disclosed is a system including an electrode and a stylet configured to steer the electrode towards its intended position during implantation, and a method for such system&#39;s use. An electrode is provided having regions with varied flexibility. A stylet having bends that are indexed to specific regions of flexibility of the electrode may be inserted into the electrode, and upon minimal radial and/or longitudinal movement of the stylet within the electrode, will cause the magnitude of the angle to which the lead is bent to either increase or decrease so as to aid the operator in placement of the electrode.

TECHNICAL FIELD

The present invention relates generally to the field of implantableelectrodes, and more particularly to a system including an electrode anda stylus configured to steer an electrode toward its intended positionduring implantation.

BACKGROUND ART

Percutaneous electrodes were introduced in the 1970's as a minimallyinvasive technique to deliver spinal cord stimulation (SCS), so as toscreen patients for satisfactory responses before implanting permanentelectrodes via laminectomy. The technique was quickly adapted forchronic implantation, and since the 1980's the majority of permanentsystems have used percutaneous rather than laminectomy electrodes.

Percutaneous SCS electrodes are inserted into the epidural space througha Tuohy type needle, bent at its tip to allow the electrode to emerge atan angle and then ascend cephalad, in or parallel to the midline. Sincethe early 1980's they have had multiple contacts, forming a linearelectrode array. Two or more can be placed in parallel to form atwo-dimensional array. Insertion is guided by intraoperative fluoroscopyand by test stimulation as the electrode is advanced in the epiduralspace. The tip of the advancing electrode is bent at an angle so that itmay be steered as it advances by rotating it, moving the tip from rightto left. Right-left positioning is critical, to such an extent that awell-placed midline electrode placed percutaneously was seen tooutperform two electrodes placed side by side, in a series of controlledtrials performed at Johns Hopkins Hospital from 2003-2005. Inengineering terms, the system (patient and stimulator) resolves smallerdimensions than the width of standard percutaneous electrodes, such thatsimply placing more electrode contacts does not substitute for preciseplacement.

Anterior-posterior position (in front of or behind dorsal epidural fat)is important, as well—not only because proximity of the electrodes tothe spinal cord increases efficiency and selectivity (of dorsal columnsvs. dorsal roots), but also because recruitment of small pain fibers inligamentum flavum (behind epidural fat) commonly causes painful sideeffects, and one way to mitigate them is to keep the electrode in frontof epidural fat and in direct contact with the dura. An experiencedoperator will attempt to keep track of which way the tip of theadvancing electrode is pointing, even on monoplanar (anterior-posterior)fluoroscopy, and attempt to direct the tip of the electrode from rightto left and from front to back.

Where SCS is to be administered by less experienced practitioners,multiple electrodes will often be used to bracket or “carpet bomb” thetarget area. Most (70-80%) percutaneous systems currently implanted havedual electrodes—in part for this reason, and in part to provideredundancy—the demonstrable inferiority of dual lead systems for commonlow back conditions notwithstanding. The best use of this technology mayin fact be to place triple electrodes, which offer potential advantageswhether they are placed perfectly, or by experienced hands (takingadvantage of transverse tripole capabilities) or imperfectly (simplyoffering redundancy).

In any of the above settings, and whether in experienced orinexperienced hands, percutaneous SCS electrode steerability is veryimportant, and none of the presently available products address itadequately. Not only must the electrode be steerable, but the steeringmust also be variable. More particularly, major steering input isrequired as the electrode emerges from the tip of a Tuohy or similarneedle, which necessarily is not parallel to the epidural space as seenin the sagittal plane. The electrode must negotiate a bend; if it doesnot bend sufficiently, it may indent the dura (or even the spinal cord).If it deviates to one side, it will still tend to continue ventrally,into the “gutter” in the lateral epidural space. Not only is there abend in the sagittal plane, there is often one in the coronal plane, asthe needle generally is not parallel to the midline, as it is insertedoff the midline to avoid the spinous processes. Thus, as the electrodeemerges it tends to deviate laterally, to one side or the other, andonce it has done so it may not be possible to steer it back to themidline. An analogy may be made with descending a steep “on ramp” ontoan icy highway which has a high crown in the center of the road and deepgutters on either side.

Once having deviated substantially from the midline, even if it issteered back, as seen on A-P fluoroscopy, the electrode may end upventral to the spinal cord and dura, and this may not be appreciatedwithout changing to a lateral fluoroscopic view.

Minor steering inputs are required after the electrode has negotiatedthe bend at the tip of the Tuohy needle and is ascending in the midline.The large bend which was an asset in negotiating the initial turnbecomes a liability, as relatively small right-left adjustments are madeas the electrode is advanced to its final position. Pointing a largebend to the left or right causes major unwanted deviations to eitherside; pointing it dorsally tends to engage dorsal ligamentous structuresand webs, at the same time moving it away from the spinal cord. Pointingit ventrally, so that it slides along the dura, pushes the duraanteriorly; this tends to be unstable, and the electrode tip may rotateand jump to one side or the other. Furthermore, when the electrode iscurved significantly in the sagittal plane its contacts are at differentdistances from the spinal cord, and stimulation thresholds varysubstantially. This frustrates test stimulation to guide placement.

Since they were first introduced in the 1970's, all percutaneous SCSelectrodes have consisted of rigid cylindrical metal contacts onflexible catheters (for example silicone elastomer, polyethylene, andmore recently polyurethane). The flexible catheter, within which areelectrical conductor(s) to the electrode contact(s), accommodatesbending, allowing for example insertion through a Tuohy needle with abend at the tip, so that the advancing assembly can negotiate the bend.The rigid contacts must negotiate the bend in the needle first, and asthey increase in length it becomes all the more difficult to negotiatethis bend, and then to steer to the target beyond.

As shown in the top view FIG. 1, a typical current, commerciallyavailable percutaneous electrode assembly (“lead”) 10 has a removable,malleable stylet 20, which may be inserted within the body of theflexible, hollow lead 10. A bend in the stylet 20 causes the lead 10around it to bend correspondingly. The stylet 20 typically is bent atthe tip—indeed, most models come with a bend already in place—andtypically the stylet may be inserted all the way to the tip of the lead10, and to the most distal electrode contact, so that the tip of thelead 10 and the electrode contacts assume a bend. The distal end of thelead 10 has a plurality of rigid electrode contacts 12, and flexiblespacer portions 13 between the contacts 12. As the bent tip is advancedunder fluoroscopic guidance it can be steered by rotating the stylet 20and/or the lead 10 so that the advancing tip deviates to the left andthe right, dorsally and ventrally, etc. As the bent tip is advanced, asseen on A-P fluoroscopy, rotating it allows it to be steered. Not onlycan it be steered right-left, it can also be steered dorsal-ventral ifthe operator follows it on lateral as well as A-P fluoroscopy (and/orkeeps mental track of its orientation using the A-P view alone). Theelectrode tip is most easily steered if it responds in a linear fashionto rotation by the operator at the other end of the lead. Further, asshown in the bottom view of FIG. 1, the bend in stylet 20 may beadvanced into and withdrawn from lead 10 so as to modify the extent towhich lead 10 bends. If the stylet 20 is not inserted fully within thelumen of lead 10, the bend of stylet 20 is located proximal to thedistal end of lead 10, resulting in a larger bend of lead 10 while thetip of lead 10 lacks stiffening and, thus, remains flexible.

Most stylets are coated with Teflon, which facilitates removal andreplacement, as is often necessary to change the bend at the tip. It istypically necessary to increase the bend to negotiate the sharp turn atthe tip of the needle, as the tip of the electrode enters the epiduralspace and must be steered to (or back to) the midline; once this hasbeen achieved, a large bend becomes a liability, as noted. The only wayto reduce the bend is to withdraw the stylet and replace it—afterstraightening it, or substituting another stylet with a smaller bend.This is cumbersome, and it can be challenging for the operator to threadthe stylet back into the tiny lumen of the lead. Some leads resist thismaneuver, and on occasion it becomes necessary to ask for a newlead—which means withdrawing the existing lead and giving up theposition achieved so far.

Electrode steerability is best if the curved electrode tip is seen onfluoro and felt by the operator's hand to move in a linear 1:1 fashionas the stylet emerging from the end of the lead assembly is rotated bythe operator's hand. A right-handed operator will generally rotate thestylet (which may rotate within the lead) or the stylet/lead assembly(which may rotate together) with his/her left hand, as the thumb andindex fingertip of the right hand advance and withdraw the body of thelead as it emerges from the hub of the Tuohy needle in the epiduralspace. Some Seldinger wire lead blanks achieve this, but no electrodeassembly does so; to varying degrees they lag, jump, and sometimes seemto wind up, as though lacking in torsional rigidity.

The malleable stylet may rotate in unison with the “lead” around it, orit may rotate within the lead, or it may (and commonly does, to varyingdegrees) do both. One presently available device may be clipped to theend of the lead so that the two necessarily rotate together (at leastwithin and adjacent to the clip; they may decouple farther away.) Thisincurs friction between the outside of the lead, along its length withinthe needle and the patient; the friction is cumulative as the lead isadvanced, and ultimately the stylet begins to rotate within the lead,thus impeding steerability. Rotation and translation of the tip nolonger track operator inputs 1:1.

Other presently available devices may have a knob at the end of thestylet, but no clip secures it to the lead; the stylet is unconstrainedand can rotate within the lead. The tip of the stylet may engage abearing within the lead tip in order to reduce friction. As the lengthof the lead and stylet assembly increases, however, the cumulative dragor friction between the outside of the stylet and the inside of the leadbody can become significant, so that the lead tip no longer tracksoperator inputs faithfully, 1:1.

Other problems and idiosyncrasies are introduced by assembly andpackaging of some available devices. For instance, if the metal styletinside the plastic lead body is bent, then the plastic lead tends totake a “set” which remains, if only temporarily, after withdrawal of thestylet. This can be useful during implantation, in that it providesfiner control over steering, but it then becomes a liability: the leadretains this bend following implantation, and so it may curveleft-right, or dorsal-ventral. With time, the curve may straighten out,with unpredictable results.

Moreover, the “set” in the plastic and the bend in the stylet are, ofcourse, pointing in the same direction when the assembly is removed fromthe package, and they remain so unless disturbed. It is very common,however, to withdraw the stylet at least in part during placement, andif this is done it may not be in phase with the lead, i.e. pointing inthe same direction, when the stylet is re-inserted. Sometimes the styletis removed and replaced, e.g. with a stiffer one, or one with adifferent bend. In To the inventor's knowledge, there is no provision toaddress this in any existing product. Marking the stylet and the lead inorder to allow alignment would be possible, but they may not be rigid intorsion, and so this might not be reliable.

Still further, the “set” in the plastic lead is, on balance, aliability. Current potential solutions include preassembling with astraight stylet, and allowing the user bend it as desired, or furnishingthe stylet separately. Presently available packages include leads thatare shipped with a bent stylet in place, incurring the above problem.

DISCLOSURE OF INVENTION

Disclosed is a system including an electrode and a stylet configured tosteer the electrode towards its intended position during implantation,and a method for such system's use. An electrode is provided havingregions with varied flexibility. A stylet having bends that are indexedto specific regions of flexibility of the electrode may be inserted intothe electrode, and upon minimal radial and/or longitudinal movement ofthe stylet within the electrode, will cause the magnitude of the angleto which the lead is bent to either increase or decrease so as to aidthe operator in placement of the electrode.

With regard to certain aspects of a particularly preferred embodiment, asystem is provided for positioning a lead within a patient, the systemcomprising a lead having a shaft with at least two electrode contactsdisposed on the shaft and a flexible spacer portion between each of theelectrode contacts, and a stylet lumen extending into the lead from aproximal end of the lead towards a distal end of the lead, along with astylet having a plurality of bends and relatively straight portionsextending between the bends, wherein the bends are positioned a distanceapart from one another so as to simultaneously align with the flexiblespacer portions of the lead when the stylet is positioned within thestylet lumen.

With regard to other aspects of a particularly preferred embodiment, amethod of using such system is provided that comprises the steps ofinserting the stylet into the stylet lumen toward the distal end of thelead a sufficient distance so that at least one of the bends in thestylet is aligned with at least one of the electrode contacts, movingthe lead within a patient in a first direction, moving the stylet in thestylet lumen so as to align such bend in the stylet with one of theflexible spacer portions so as to change the angle of at least a portionof the lead, and further moving the lead within the patient in a seconddirection different from the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous advantages of the present invention may be betterunderstood by those skilled in the art by reference to the accompanyingdrawings in which:

FIG. 1 is a side view of a prior art multi-contact lead and a bentstylet engaging such lead.

FIG. 2 is a side view of a system comprising a multi-contact lead andstylet according to certain aspects of a particularly preferredembodiment of the invention.

FIG. 3 is a side view the system of FIG. 2 showing the effect of variedflexibility of portions of a lead on bending of the lead.

FIG. 4 is a side view of the system of FIG. 2 showing further effects ofvaried flexibility of portions of a lead on bending of the lead.

FIG. 5 is a side and various cross-sectional views of the lead of FIG. 2with varied configurations of flexible spacer portions.

FIG. 6 is a side view of the lead of FIG. 2 with a segmented electrodecontact.

FIG. 7 is a side and various cross-sectional views of the lead of FIG. 2with further varied configurations of flexible spacer portions.

FIG. 8 is a side, cross-sectional view of the lead of FIG. 2 depictingvarious configurations of asymmetric spacer portions and electrodecontacts.

FIG. 9 is a side view of certain lead configurations of FIG. 8 showingthe effect of such configurations when subjected to bending from a bentstylet.

FIG. 10 is a side view of the lead of FIG. 2 showing variousconfigurations for indexing a stylet and an associated lead.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

The following description is of a particular embodiment of theinvention, set out to enable one to practice an implementation thereof,and is not intended to limit the preferred embodiment, but to serve as aparticular example thereof. Those skilled in the art should appreciatethat they may readily use the conception and specific embodimentsdisclosed as a basis for modifying or designing other methods andsystems for carrying out the same purposes of the present invention.Those skilled in the art should also realize that such equivalentassemblies do not depart from the spirit and scope of the invention inits broadest form.

As shown in FIG. 2, a flexible lead 10 comprising a multicontactelectrode is provided with an electrode array having rigid electrodecontacts 12 separated by flexible spacer portions 13, typically ofuniform length. A stylet 20 is also provided which, when such stylet isinserted into flexible lead 10, is configured to cause the lead 10 tobend. As the stylet 20 is advanced within flexible lead 10, lead 10 willconform to the stylet 20 and the bend will advance. To the extent thatthe lead is inflexible, it will not conform to the bend in the stylet,and in the extreme case in which it is completely rigid, e.g. acylindrical electrode contact of sufficient length, within which thestylet is constrained by the inside diameter, it will not bend at all.

In accordance with one aspect of an embodiment of the invention, stylet20 is provided preferably multiple focal bends 22, which are relativelyacute (i.e., having a relatively small radius or curvature), withrelatively straight (i.e., having a large to infinite radius ofcurvature) segments between focal bends 22, the dimensions of which arepreferably chosen so that one or more of the bends may be made to lineup with the flexible spacer portions 13 when the stylet is inserted tojust the right depth of flexible lead 10. This will cause the tip of theelectrode array to bend to the maximum degree, as shown in the middleillustration of FIG. 2. When the stylet 20 is moved to a position inwhich its bends are within the rigid electrode contacts 12 and itsrelatively straight sections are within the flexible spacer portions 13,this reduces the bend in the array to a minimum, as shown in the bottomillustration of FIG. 2.

As shown in FIG. 2, bends 22 (two are shown in FIG. 2) may be positionedso as to lie within flexible spacer portions 13 of lead 10, causing thelead 10 to bend, or within a rigid segments, in this case the electrodecontacts 12, minimizing the resulting bend in lead 10. Although a singlebend will create a bending effect, the exemplary embodiment depicted inFIG. 2 shows two bends 22 in series, with identical and complementaryspacing of electrode contacts and flexible spacer portions, so that theeffects are cumulative or additive. When the bends in stylet 20 are inphase with the flexible spacer portions 13, the assembly bends; whenthey are out of phase with the flexible spacer portions 13, the assemblystraightens.

The phase of one or more bends 22 in stylet 20 with respect to theflexible spacers and the rigid electrode contacts of the electrodearray, as its longitudinal position is varied, determines the magnitudeof the bend of the assembly.

Although the contacts 12 and flexible spacer portions 13 are of uniformlength in the exemplary embodiment depicted in FIG. 2, such that thespacing between stylet bends 22 is equal to the sum of one contact andone spacer length, this need not be the case. Those of ordinary skill inthe art will recognize that there are multiple possible variations inthe lengths of each of these elements that may allow the rigid andflexible elements to interact with the bends in the stylet so as toincrease or reduce the curvature of the assembly at one or more pointsalong its length. Common to all is the interaction of the relativelyacute stylet bend with the relatively flexible spacer at one or morepoints. Also common to all, and a benefit of the instant invention, isthe ability to vary the bend in a flexible lead 10 (in particular at ornear the tip, within or near the electrode contacts 12) by moving thestylet 20 within the lead 10, without changing its bend, removing it, orreplacing it, resulting in significant convenience for the operator.

In accordance with another aspect of a preferred embodiment of theinvention, and with particular regard to FIG. 3, flexible lead 10, orspecific portions thereof, may be provided in varying degrees offlexibility, which in turn will affect the extent to which stylet 20will cause flexible lead 10 to bend when it is inserted into lead 10. Asshown in FIG. 3, the flexible lead shown in the top illustration is lessflexible than the flexible lead shown in the bottom illustration. As aresult, when an identically bent stylet 20 is inserted in either of thetwo flexible leads 10 shown in FIG. 3, the more flexible conforms morereadily to the bend in the stylet 20, approaching the angle of theoriginal bend in the stylet 20, while the more rigid lead 10 bends less.

Next, as shown in FIG. 4, a single flexible lead 10 may be provided withsegments of different flexibility. In the exemplary embodiment shown inFIG. 4, the two spacer portions 13A and 13B nearest the tip of theelectrode are more stiff (less flexible), and the two spacer portions13C and 13D further from the tip are less stiff (more flexible). Thus,as stylet 20 with a particular given bend is advanced into flexible lead10, when the bend encounters the more flexible spacer portions 13C and13D, the lead 10 bends maximally. When the stylet 20 is advanced furtherinto the more rigid spacer portions 13A and 13B at the tip of the lead10, the bend is minimal.

Those of ordinary skill in the art will thus recognize from theforegoing that the flexibility of spacer portions 13 in a flexible lead10, as well as the flexibility of the electrode contacts 12 (asdiscussed in more detail below), may be varied at any position along thelength of the lead 10, giving any particular segment more or lessoverall flexibility. A stylet bend traversing this segment will causethe lead 10 to bend correspondingly more or less. Thus, a wide varietyof flexible lead configurations may be provided whose varying degrees offlexibility may be particularly well suited for specific applications.As shown in FIG. 4, two relatively stiff spacer portions 13A and 13B andtwo relatively flexible spacer portions 13C and 13D may be used withpresumably stiff electrode contacts 12, although this is merely onepossible example, and the numbers of electrode contacts and spacerportions, and their flexibility, may vary without departing from thespirit and scope of the invention.

Once again, a benefit of the instant invention is to allow the operatorto vary the bend in the lead by simply repositioning the stylet 20within flexible lead 10, instead of requiring the operator to, forinstance, remove and reconfigure the bend and thereafter attempt toreplace the stylet 20 within the lead 10. In the particular exampleshown in FIG. 4, the operator may use the maximum bend to negotiate thesharp turn at the tip of the needle entering the epidural space, andthen advance the stylet 20 within the lead to reduce the bend for finersteering adjustments as the procedure continues. This allows theoperator to vary the bend at the tip of the lead 10 by simply moving thestylet 20 longitudinally a small amount. This avoids the cumbersomeprocess of withdrawing the stylet 20 from the lead 10 to change itsbend.

Relatively small radius bends are shown in the representative Figuresfor illustrative purposes. In practice, those of ordinary skill in theart will recognize that the radius of the bend should be large enough,and the stylet 20 should be flexible enough, to advance and withdrawthrough the inside diameter of the lead 10. Those of ordinary skill inthe art will also find it beneficial to mark or index the stylet 20and/or the lead to indicate their relative positions (visibly and/orpalpably), and in some applications to secure the stylet with respect tothe lead to maintain their relative positions, as discussed in greaterdetail below.

Next, FIG. 5 shows various configurations for altering the flexibilityof spacer portions 13 in lead 10. A typical lead segment 13E consists ofa cylindrical tube or catheter segment. However, the flexibility of anygiven catheter segment may be modified in a number of ways. First, theconfiguration of the lead segment may be varied without changingmaterials (as shown in optional cross-sectional views of segment 13F) byrelieving or removing portions of the inner wall, such as by addinggrooves or ridges, or substituting another form of the same materialsuch as foam, to reduce durometer and increase flexibility, bycomparison with a full thickness wall. Moreover, the materials of whicha spacer segment is comprised may be modified, such as by using materialof different durometer, such as silicone elastomer instead ofpolyurethane. Still further, materials may be combined, for examplesilicone elastomer inside of polyurethane, or for example addingstiffening elements, which may simply resist bending or may function astension or compression elements in a beam, as shown at the bottomillustration of FIG. 5. Wires (which may or may not function aselectrical conductors) or stylets may be added as well to varyflexibility.

Moreover, and with reference to FIG. 6, flexibility of electrodecontacts 12 may likewise be modified. In the example shown in FIG. 6,this may be accomplished by segmenting electrode contacts 12. Where aseries of N electrode contacts 12 are provided in a linear array, onesuch contact at a particular distance from the tip of the lead 10 (i.e.,where increased flexibility is desired) may be replaced with n (two ormore) shorter electrode contacts 12A, the lengths of which preferablysum to less than the length of the original electrode contact 12. Thedifference in length is made up by flexible spacer portions separatingthe shorter electrode contacts (for purposes of this example, althoughnot necessarily or in general, as lengths may vary). If the electrodecontacts 12A are connected in parallel, together they will constitute asingle virtual electrode contact, the position of which will beequivalent to that of the larger electrode contact 12. Local currentdensity at the individual segments will be a bit higher, but currentdensity will be the same several millimeters away, e.g., at the spinalcord. Impedance will be a bit higher, as well. The virtual electrodecontact will preferably have the same length as the original electrodecontact, and so the uniformity of electrode contact spacing bycomparison with the original can be preserved.

The individual electrode contact segments could optionally be connectedto the generator individually, and programmed as such, increasingspatial resolution, but current density would be much higher (at least ntimes higher, exceeding n to the extent flexible spacer portions replacecontact surface). The segments could be distinguished as N1, N2, etc.,and would occupy the position originally occupied by electrode contactN.

As noted above, the multiple short electrode contact segments 12A arepreferably connected in parallel, i.e., wired together, for example withspiral conductors, to function as one longer contact with internalflexibility, giving this segment of a multicontact array moreflexibility.

While not shown explicitly in the drawings, it is also envisaged thatthe joints between electrode contacts 12 and spacer portions 13 maythemselves also be flexible, and such flexibility may be varied, for thesame purposes as described above.

Next, as shown in FIG. 7, radial asymmetry may also be used to vary theflexibility of segments of lead 10. More particularly, while allcommercially available percutaneous electrode contacts known to theinventor herein are cylindrical, and thus in cross-section are radiallysymmetric, FIG. 7 shows the general case of an asymmetrical spacer, andFIG. 8 shows specific examples of variously asymmetrically configuredspacers and electrode contacts, which may be used to alter theflexibility of segments of lead 10.

As shown in FIG. 7, by constructing a lead 10 so that, as seen in thecross-sectional view of illustration (a) of FIG. 7, one side 13A is oflower durometer than the other side 13B, then it will bend more readilytoward this lower durometer side. Thus, if the bend in a stylet istoward the low durometer side 13A, the assembly will bend maximally; ifit is turned 180 degrees, toward the high durometer side 13B, it willbend minimally. The concept of “phase” as discussed above may beintroduced again, this time radially: the stylet may be rotated so thatthe bend is in phase with the preferred bend of the lead, for maximalbending of the assembly. It may be rotated 180 degrees out of phase forminimal bending. It may be rotated to intermediate positions forintermediate bending.

As shown in FIG. 7, the asymmetric cross-section of the lead 10 may beachieved in a number of different ways, to the same effect. If thestylet lumen (which may be considered as the inside diameter of a singlelead catheter or as one catheter inside another) is concentric with theoutside of the lead, then the materials on one side and/or the other maybe chosen to resist tension or compression, achieving the requisiteasymmetry. If the stylet lumen is off-center, as shown in illustration(b), so that the wall thickness varies from one side to the other, thisconfers asymmetry. In practice, there will be at least one electricalconductor within the lead, all the way to the tip contact; and therewill be more and more proximally, to serve additional electrodecontacts; these conductors can be arranged so that they function asmechanical elements, to confer asymmetry.

As was the case with the longitudinally phased example described above,the radially phased example of FIG. 7 allows the bend at the tip of lead10 to be varied by small movements of the stylet 20; in this case,rotary movements. Once again, this avoids the need to re-bend, remove,or replace the stylet 20.

Similarly, such asymmetric cross-section of lead 10 may be achieved byway of wedge-shaped electrode contacts and complementary interveningflexible, compressible plastic (e.g., polyurethane) spacer portions,examples of which are shown in the various cross-sectional views of FIG.8, which by virtue of the longer compressible segments between theshorter side(s) of the contact segment(s) allow the assembly to bendmore easily in this direction, to a greater (more acute) angle. Thiswill facilitate steering when a more pronounced bend is needed, e.g.,when the electrode array first emerges from the end of a Tuohy needleinto the dorsal spinal epidural space.

As used here, the term “wedge” refers generically to a shape which, asseen from either side, is longer at one edge and shorter at the otheredge. The sloping contour from one edge to the other may be straight,curved, sawtooth, etc. The term “wedge” should also be considered toencompass shapes in which the height at one edge is zero, and even onein which there is a gap, so that the contact does not encircle the full360 degree circumference of the catheter.

Turning a bent stylet 180 degrees within the body of lead 10, thusreversing its direction and causing the bend to reverse, will causeequal and symmetric bending of the electrode assembly if the contactsand spacers are cylindrical and of uniform material. If, on the otherhand, wedges are provided in lead 10 as generally shown in FIG. 8,rotating the bent stylet tip toward the side or edge with the shorterportion of metallic electrode contact segments 12 and the longercompressible plastic spacer portions will allow a more pronounced bend,as this side is more compressible.

Rotating the stylet 180 degrees so that the bent tip is toward theshorter plastic spacer portions and the longer electrode contactsegments will result in a less pronounced bend, as this side of theassembly is less compressible, thus providing for a straighter tip formore subtle steering, as when nearing target level. Intermediate anglesof rotation will produce intermediate bends. All of such varied bends inlead 10 may be accomplished without requiring that the operator withdrawor replace the stylet.

It is noted that ancillary benefit may be had by providing contacts insuch wedge-shaped configurations beyond providing controlled curvatureof lead 10 in response to radial movement of a stylet within such lead.More particularly, the narrow part of a wedge may still function as anelectrode; thus, in spinal cord stimulation applications, if the narrowside of the wedge-shaped electrode contact is placed towards the dura,and the wider part toward the ligamentum flavum, this will reduce localcurrent density and thus may reduce painful side effects. Moreover, thewedge electrode contacts on a cylindrical catheter may provide it theattributes of a “percutaneous paddle,” while being forgiving of invertedplacement.

Next, as shown in FIG. 9, various configurations of electrode contacts12 are shown. In illustrations (a) and (b), electrode contactconfigurations are shown that are visibly (and thus radiographically)asymmetric, while in illustration (c), electrode contact configurationsare shown that are not visibly asymmetric. Regardless, common to eachsuch configuration is the visible change in bend as the stylet isrotated in and out of phase, as depicted in the bottom two illustrationsof FIG. 9. More particularly, as shown in illustration (d) of FIG. 9, asstylet 20 is rotated in lead 10 to an out of phase orientation, aminimal bend results in lead 10. In contrast, as shown in illustration(e) of FIG. 9, as stylet 20 is rotated in lead 10 to an in phaseorientation, a maximum bend results in lead 10. Notably, whether theleads 12 are visibly asymmetric or not, the bend that results in lead 10when stylet 20 is rotated is radiographically visible, thus aiding theoperator in maintaining proper orientation during insertion of the lead10.

As shown in FIG. 10, in order to further assist the operator inmaintaining proper orientation during insertion of the lead 10, theradial position of a stylet with respect to lead 10 may be indexed.Rotation of a stylet 20 within lead 10, as well as rotation of the twotogether or separately, may be significant with the radially asymmetricdesigns shown herein. Thus, a point or radial position 14 on thecircumference of the connector end 18 of the lead may be marked, whereit is visible to and palpable by the operator. Similarly, as shown inthe bottom illustrations of FIG. 10, the handle (or knob or loop) on thestylet may be marked to indicate the direction of the bend in stylet 20.In the exemplary illustration of FIG. 10, there is a loop at the backend of stylet 20 (the end manipulated by the operator) which points inthe same direction as the bend in the front end or tip of stylet 20.

In use, and by way of non-limiting example, the bent stylet 20 may beinserted into the radially asymmetric lead “in phase” to achieve themaximal bend. The operator would pass the assembly through the Tuohyneedle with the bend directed left or right as appropriate. The bend(and perhaps wedges, if present) will be visible in profile as theelectrode tip emerges from the tip of the needle and negotiates the turnout of the needle, which is the most difficult corner of all. The styletmay then be rotated out of phase with the lead as a smaller bend isrequired thereafter.

It is believed that the present invention and many of its attendantadvantages will be understood by the forgoing description. It is alsobelieved that it will be apparent that various changes may be made inthe form, construction and arrangement of the components thereof withoutdeparting from the spirit and scope of the invention or withoutsacrificing all of its material advantages. The form herein beforedescribed is merely an explanatory embodiment thereof.

INDUSTRIAL APPLICABILITY

The present invention is applicable to surgical medical devices andrelated methods. The invention discloses an electrode and stylus andrelated method configured for aiding in the placement of such electrodeat a desired location within a patient's body. The device can be made inindustry and practiced in the medical field.

I claim:
 1. A system for positioning a lead within a patient, comprising: a lead comprising a shaft having a plurality of electrode contacts disposed thereon and a flexible spacer portion between each of said electrode contacts, said shaft having a section defining a cylindrical exterior wall, which section includes at least one of said electrode contacts and at least one of said flexible spacer portions, which section has a uniform outer diameter along the length of the section, and a stylet lumen extending into said lead from a proximal end thereof towards a distal end thereof, wherein one or more planar cross-sections through said lead taken in a direction perpendicular to a major axis extending lengthwise through a center of said lead and through said section defining a cylindrical exterior wall include a portion of said at least one electrode contact and a portion of said at least one flexible spacer portion, and wherein said portion of said at least one electrode contact is asymmetrically positioned with respect to said major axis in said one or more planar cross-sections; and a stylet having a plurality of bends therein and relatively straight portions extending between said bends, wherein said bends are positioned a distance apart from one another so as to simultaneously align with said flexible spacer portions of said lead when said stylet is positioned within said stylet lumen; wherein a first one of said flexible spacer portions has greater flexibility than a second one of said flexible spacer portions, such that one of said bends in said stylet engaging said first one of said flexible spacer portions will cause said lead to bend at a larger angle than said one of said bends in said stylet engaging said second one of said flexible spacer portions.
 2. The system of claim 1, wherein said first one of said flexible spacer portions comprises a cylindrical wall having a first thickness, and a second flexible spacer portion comprises a cylindrical wall having a second thickness that is greater than said first thickness.
 3. The system of claim 1, wherein said first one of said flexible spacer portions is formed of a first material, and said second flexible spacer portion is formed of a second material, wherein said first material has a greater flexibility than said second material.
 4. The system of claim 1, said second flexible spacer portion further comprising at least one stiffening insert embedded within said second flexible spacer portion.
 5. The system of claim 1, wherein at least a first one of said electrode contacts has a first length L, and at least two second electrode contacts each have a second length that is less than L/2, and wherein said first flexible spacer portion is positioned between said first one of said electrodes and one of said second electrodes, and said second flexible spacer portion is positioned between said at least two second electrodes.
 6. The system of claim 5, wherein a combined length of two of said second electrodes and said second flexible spacer portion equals L.
 7. The system of claim 1, wherein said system is configured such that aligning said one of said bends in said stylet with said first one of said flexible spacer portions will cause said lumen to bend at an angle, and rotation of said stylet within said stylet lumen when said one of said bends in said stylet is aligned with said first one of said flexible spacers will cause the magnitude of said angle to vary.
 8. The system of claim 7, wherein said first one of said flexible spacer portions further comprises a cylindrical section formed of compressible material having a top side and a bottom side opposite said top side, and wherein said top side has a first durometer rating and said bottom side has a second durometer rating different from said first durometer rating.
 9. The system of claim 7, wherein said first one of said flexible spacer portions further comprises a cylindrical section formed of compressible material, and wherein said stylet lumen extends through said first one of said flexible spacer portions along an axis that is set off from a central axis of said at least one flexible spacer portion.
 10. The system of claim 7, wherein at least one of said electrode contacts is radially asymmetric such that a first side of said at least one electrode contact is of a greater length than a second side of said at least one electrode contact opposite said first side, and wherein said first one of said flexible spacer portions is adjacent said at least one electrode and has a radially asymmetric configuration that is complementary to said at least one electrode contact.
 11. The system of claim 7, said stylet further comprising an indicia configured to indicate both a radial orientation and a longitudinal orientation of said stylet with respect to said stylet lumen.
 12. A method of using the system of claim 1, comprising the steps of: inserting said stylet into said stylet lumen toward said distal end of said lead a sufficient distance so that at least one of said bends in said stylet is aligned with at least one of said electrode contacts; moving said lead within a patient in a first direction; moving said stylet in said stylet lumen so as to align said one of said bends in said stylet with one of said flexible spacer portions so as to change the angle of at least a portion of said lead; and further moving said lead within said patient in a second direction different from said first direction.
 13. The method of claim 12, further comprising the steps of: further moving said stylet in said stylet lumen toward said distal end of said lead so as to further change the angle of at least a portion of said lead; and further moving said lead within said patient in a third direction different from said second direction.
 14. The method of claim 12, wherein said step of moving said stylet in said stylet lumen further comprises rotating said stylet within said stylet lumen.
 15. The method of claim 14, wherein rotation of said stylet within said stylet lumen causes a magnitude of an angle to which said lead is bent to vary. 